Tube still or heater and the like



Web 24, 13

P. QSTERGAARD TUBE STILL OR HEATER AND THE LIKE Filed May 24, 1955 4Sheets-Sheet PW flsi'ergaarcl,

24, 1936. P. OSTERGAARD TUBE STILL OR HEATER AND THE LIKE} Filed May 24,1955 4 Sheets-Sheet 2 9 193.. P. OSTERGAARD TUBE STILL 0R HEATER AND THELIKE Filed May 24, 1935 4 Sheets-Sheet 5 M WM W 2 7 n w H 5% MM a w juwlr v fi a w w M a M a m E r N- W M 5 6 5 w 2W L 6%? S 2 \5/ F/ EEE g 6M? .mu mwmmmvfl flaw W 1 E fi N mm 2 q i A w M a a H936. F. OSTERGAARDTUBE STILL OR HEATER AND THE LIKE Filed May 24, 1955 4 Sheets-Sheet 4 Q\=\S K Patented Mar. 24, 1936 UNITED STATES TUBE STILL OR HEATER AND THELIKE Povl Ostergaard, Mount Lebanon, Pa., asslgnor,

by mesne assignments, to Gulf Oil Corporation of Pennsylvania,Pittsburgh, Pa., a corporation of Pennsylvania Application May 24, 1935,Serial no. 23.331

11 Claims. (01.122-356) This invention relates to tube stills or heatersand the like and it comprises a tubular heater in the form of a cage ofinterconnected tubes in banks situated within a furnace and adjacent toa plurality of burners, the latter being so arranged within the firechamber that radiant heat is uniformly and efllciently applied to thetubes,

elf ctive utilization of radiation is increased, a

greater portion of the generated heat is absorbed,

and a radiant heater of greater capacity can be constructed, all as morefully hereinafter set forth and as claimed.

In small capacity tube heaters the most ellicient construction is thatin which one burner,

axially located, radiates heat directly upon vertical tubes lining theWalls of a cylindrical fire chamber, or furnace. As the burner isequidistant from all tubes and the flame radiates heat in everydirection, the tubes are uniformly heated and the radiant energy emittedby the flame is efficiently absorbed by the tubes. However, when thecapacity of the heater is increased v as by increasing the number oftubes and enlarging the fire chamber, one burner becomes inadequate anda plurality of burners in such a fire chamber cannot be positioned to.give maximum radiation upon the tubes. Unsymmetrical arrangement ofburners in a cylindrical furnace gives irregular radiation, and asymmetrical arrangement of more than two burners in the center of acylindrical furnace gives rise to an excessively hot core of gasesleaving the radiation furnace, In prior large capacity heaters of thistype three or more burners have been located at uniform intervals on aninner circle concentric with the circle formed by the furnace walls. Asthe flame of each burner radiates heat in every direction, symmetricalarrangement of several burners about an axial point results indevelopment of a highly heated core of gas at the center of the group.Thus in the case of cylindrical heaters having three burners groupedsymmetrically about the axis, the burners are at the points of anequilateral triangle and each flame shields the tubes from radiationfrom the other flames, to a certain extent. Inthe center of a group ofburners, there is a central core of gas which has passed through and outof its luminous or radiant stage without loss of heat content such ashasv so taken place in the case of other portions of the flame. Theheated core tends to rise swiftly and thereby carry heat out from thefurnace proper. The result is that a large portion of the heat generatedin the furnace is recoverable only by 55 convection. The central core ofsuch gas comes into being when three burners are symmetricallypositioned about an axis, and this central core represents an increasingproportion of the total generated heat as the number of burners is in-'creased above three. Many advantages, includ- 5 ing very great economyin original construction and subsequent maintenance, are attainable whenthe radiant heat generated by the burners can be efliciently transferredto the material which is to be heated, but when three burners are sym-10 metrically arranged only a fraction of the radiant heat of the burnerflames can be transferred as radiation. When a. larger number of burnersare symmetrically arranged utilization of the flame radiation is evenless eflicient. 15

Heaters of the type to which this invention relates have asuperstructureconsisting of a top arch and a stack or flue, andsometimes either a convection heater and an air preheater, or both. Allof these are supported above the tube 20 chamber. This superstructurerequires a-supporting frame consisting of vertical columns spanned bysuitable structural members. As the tube area ofa cylindrical tube stillis increased, the diameter of the cylinder formed by the walls 25 of thefire chamber is necessarily increased proportionally. The verticalcolumns must be placed on the outside of the walls, and hence the spanbetween the columns is increased with increased diameter of the heater;the result being 0 that the construction of suitable members to span thecolumns becomes increasingly diflicult and expensive. When a hot core ofgases is formed in the fire chamber, a large convection heater isrequired to absorb the heatconveyed by those 35 gases: the size of thisheater further complicates the superstructure. If the convection heateris' omitted the available heat is wasted and operation becomesuneconomical.

A convection heater ordinarily consists of 9.40 rectangular bank oftubes, and, as this shape does not conform to the circular shape of thechambers discussed, the passage connecting the two must necessarily varyin cross section from circular at one end to rectangular at the other.45 The construction of such a passage is highly involved and the designunwieldy. When such a passage is used the length of the convectionheater tubes is limited. It is necessary that the diagonal dimension ofthe convection heater be less than the diameter of the tube circle ofthe radiant heater; this to provide access to the ends of the tubes ofthe radiant heater for purposes of inspection, cleaning, andreplacement.

An object of the present invehtion is the provision of a tube still orheater having a large capacity and having a plurality of burners and oneor more banks of tubes uniformly and closely spaced from the burners, sothat the radiant heat produced by the burners is uniformly absorbed bythe tubes, and formation of a heated core of gases is obviated. Thebanks of tubes are arranged in a sort of cage surrounding the burners.Usually the tubes are arranged vertically; sometimes they are arrangedhorizontally, or some vertically and some horizontally.

Another object of the invention is the provision of a multi-burner tubestill capable of utilizing radiant heat from the burners with maximumefliciency and having a fire chamber of such a shape that the capacitymay be increased without increasing the distance between burners andtubes and without increasing the span between columns supporting thesuperstructure, and whereby such an increase of capacity does notcomplicate the construction for supporting the superstructure. Thelength of the furnace is increased without proportional increase of itswidth.

Another object of the invention is to provide a multi-burner firechamber, capable of utilizing radiant heat from the burners withgreatest efficiency and the shape of which conforms in general to theshape of a rectangular convection heater supported above it so that thepassage connecting the two may be of simple design. The tubes in theconvection heater may consequently be fully utilized, and they may be ofgreater length than has been practical with circular fire chambers.

A further object of the invention is the provision of a multi-burnertube still wherein a convection heater may be employed to absorb thenonradiant component of the heat generated by the burning gases withinthe furnace which has not been completely absorbed by the still tubes,and wherein the convection heater can be kept to minimum size.

In the drawings;

Fig. 1 is a vertical section along the major vertical axial plane of anelongated vertical tube still with air preheater, and shows thearrangement and shape of the various elements according to oneembodiment of my invention;

Fig. 2 is a horizontal section taken along the line 2-2 of Fig. 1, andshows the elongated shape of the fire chamber, semi-circular end walls,and the relative position of the burners and tubes;

Fig. 3 is a vertical section of a tube still similar to that shown-inFig. 1, but this still has straight end walls and has a convectionheating section interposed between the preheater and the fire chamber;

Fig. 4 is a horizontal section taken along line 4-4 of Fig. 3 and showsthe elongated fire chamber of rectangular shape;

Fig. 5 is a diagrammatical plan and shows one form of tube arrangementin the fire chamber, wherein the tubes are subdivided into separateheating imits, and passage of liquids through separate units isindicated;

Fig. 6 is a diagrammatic view in elevation showing the tube arrangementof Figure 5 surmounted by a convection heater, and also showing onemethod of connecting the tubes in the convection heater to those in thefire chamber;

Pig. 7 is an elevation taken on line 1-1 of Fig. 6 showing theconvection heater of that view, and also showing a manner of dividingthe convection heater into separate units for preheating different m;

being of the same length and positioned in a row, 7

parallel to one another, with all of their upper ends in one horizontalplane. The heater 8 is designed to heat fluid circulated through thetubes, the heat emanating from combustion of fluid fuel supplied by aplurality of burners 21. The burners serve as means for producingradiant heat. The flames from the burners rise in the furnace andradiate heat in all directions, but principally laterally by reason oftheir naturally elongated nature. The heater may consist of one row, ormore than one row of tubes, and at least one row of these tubes willcompletely surround the plurality of burners which furnish the source ofheat. Figs. 2 and 4 and 5 depict two complete rows 50 and 5|, eachtotally surrounding the burners 21. In some respects this appears mostclearly in Fig. 5.

In my invention I place the burners 21 in a straight row and the closestrow of tubes 50 is positioned symmetrically about the burners 21 at adistance therefrom proper for efiicient combustion and proper for mostefiective radiation of heat to said tubes 50. The spacing betweenburners is approximately the same as the spacing between the row ofburners and the tubes. If the inter-burner interval is made much greaterthan the separation between the burner row and the tube row, tubesdirectly opposite the burners receive a disproportionately largefraction of the heat from the burner as compared to tubes midway betweenburners. 0n the other hand, spacing the burners very close together doesnot provide an increase in heating capacity proportionate to theincrease in number of burners. A second row of tubes 5| is preferablypositioned in back of row 50. The tubes of this second row arepositioned to receive maximum radiation of heat from the burning fueland to provide a maximum shielding effect for the walls ID of theenclosing furnace.

The burners are substantially equidistant from the tubes which absorbthe heat. The end burners in the row are positioned at a distance fromthe end walls equal to their spacing from the side walls. As the burnersare placed in a straight line, mutual screening of radiation by theburners is minimized and the radiant heat produced by each flame isradiated upon and is absorbed by the closely adjacent tubes.

The tubes of the heater 8 are seriately connected to one another to formbanks, as banks 36, 31, 38, and 39 of Fig. 5, and the oil to be heatedis circulated through these banks to ab,- sorb the heat radiatedthereto. Separate banks, either adjacent or remote, may be seriatelyconnected, or separate streams of liquid to be heated may be circulatedthrough separate banks of tubes. Any number of tubes in any portion ofany row may be seriately connected into a bank but ordinarily a bankwill consist of a number of adjacent tubes as illustrated by thearrangement of header connection I! in Fig. 5.

As previously stated my invention comprises aosass'r a heater 8 having aplurality of burners 21 and these are positioned in one straight line.These burners serve as sources of heat. In positioning the tubes aboutthe line of burners, to receive radiated heat from burner flames, therow of tubes is arranged in an oblong rectangle or in an oblong havingparallel straight sides and substantially semicircular ends. The formerof these is shown in Fig. 4 and the latter is shown in Figs. 2 and 5.The spacing of the tubes from the burners has already been described.

The heater 8 is enclosed within a furnace comprising side walls 9, endwalls I8, a furnace floor l3, and roof l2. All of these are ofrefractory material. The burners 21 open into the furnace throughrefractory cones 28 in the furnace floor l3. A central portion of thefurnace roof i2 is developed as upturned section l5 into a passageway i8for directing the combustion gases from the furnace toward a stack 28.The tubes of the heater 8 project through the furnace roof l2 and floorI3 for a distance suflicient to make the return headers l4 accessiblefrom the outside of the furnace, thereby permitting convenientinspection and cleaning of the tubes.

In all embodiments the tube banks form a. sort of cage surrounding theburner row, the walls of the cage being substantially equally spacedfrom the burner row.

Positioned in the path of the combustion gases, between the furnace andstack 28 is an air preheater H. such a preheater is shown in Figs. 1 and3. It comprises a bank of parallel tubes IS, the openings of whichprovidecommunication between passage l6 and stack 20. Com.- municationbetween l5 and '20 is otherwise obstructed by lower tube sheet 52 andupper tube sheet 53. These metallic tube sheets 52 and 53 are pierced toreceive the tubes l8 and the tubes l8 are fastened into and supported bythese tube sheets. Tube sheets 52 and 53, together with peripheral shell33 serve to enclose a chamber 54 through which air is directed forpreheating before directing it to the burners 21. The air preheater maybe provided with bafil es I9, if desired, for the usual purpose of suchdevices. A

blower 2| is provided to force air through conduit 22 to the preheaterl1 and thence by way of conduit 23 to burners 26.

The principal heater 8 is designed to receive and absorb a maximumportion of the available heat as radiant heat. Not all the heat of aburner flame is in the form of radiant energy, and in certain cases itis advantageous to incorporate a convection section into my tube stillto absorb the remaining available heat of the combustion gases. In suchcase, as shown in Figs. 3 and 6, I interpose a convection section 24between the heater 8 and the air preheater l'I.

Referring to Fig. 3, an advantageous form of construction is shownwherein a convection heater 24 is interposed between heater 8 andpreheater I'I. The heater 24 comprises a bank of horizontal tubes 25disposed lengthwise of the elongated fire chamber 8 and connected insuch manner that liquid may be circulated through the tubes 25 in heatexchanging relationship with hot gases rising from 8. The tubes 25 maybe'connected all in series or connected in separate groups as shown inFig. 7. This convection section 24 may be used to preheat a stream onits way to radiant heater 8, as shown in Fig. 6 or it may be used as asort of soaking coil for a stream which has been previously heated inradiant heater 8, or it may be used independrefractory burner cones 26of conical shape opening outwardly at the top. At the lower, narrow endeach cone is provided with a suitable burner 21 of any well known typesuitable for the particular fuel to be burned. Each burner receivesfuel, from a source not shown, and preheated air from conduit 23 forcombustion of said fuel. As-illustrated best in Figs. 1, 2, 3, and. 4,the burner cones are positioned at uniform intervals in a horizontal rowalong the major vertical axial plane of the space enclosed by heater 8.This places the row of burners centrally with respect to the tubes lllining the side walls 9 of the furnace, and the end burners aresubstantially the same distance from the tubes lining the end walls illof the furnace. The tubes adjacent to the end walls it! may be moreuniformly heated by arranging them in a semi-circular row about the endburner as axis. The walls 9 and 10 of the furnace are supported byvertical columns 28 placed at intervals around the walls adjacent to theoutside faces thereof and resting on suitable foundations such as 29.The furnace floor l3 and the burners 21 are shown as supported byupright members 38 resting on foundations 3|. The stack is supported bybeams 32 spanning the upright columns 28 both lengthwise and crosswise.The roof members l5 and i2 are braced by irons 34. The upper and lowerreturn couplings M of the tubes are advantageously enclosed withinhousings 35 to prevent loss of heat through radiation.

When more than one row of tubes II are used in the heater 8, the tubesin each row may be so spaced as to receive a definite desired share ofthe total heat output from the burners and hence the degree of heatingin each row may be con-. trolled. Furthermore, the tubes ll may besubdivided into separate heating units' differing from each other intotal tube lengths and-in the manner in which the various tubes in theunit are connected, and in this way different stocks may be concurrentlysubjected to separate and unlike treatment in the radiant heater 8.

Figs. 5, 6, and 7 illustrate diagrammatically one specific arrangementof the tubes of heater 8-and of convection heater 25. This. particularconstruction may be employed to advantage in a cracking still forpetroleum stocks requiring difierent heat treatments during cracking.According to this arrangement the tubes II are divided into fourdifferent banks denoted in Figs. 5 and 6.by reference characters 36, 31,38, and 39. Tube bank 36 may be used to crack stock which is to besubjected to relatively slight heat treatment, such stock entering inlet48 and passing first through the outer row of tubes and then the innerrow and finally leaving the heater 8 through outlet 4|. The entire bankof tubes 38 is heated mainly by two burners and these burners may befired at a lower rate than the. other burners to prevent overheating ofthe stock undergoing treatment in group 36. Tube banks 31 and 38 arearranged for cracking gas oil and are connected to convection heater 24by pipes 42 and 43 respectively. The convection heater 24 can beconstructed as two separate banks and is so shown in Fig. '7 withseparate inlets 44 and 45. Gas oil introduced through inlet 45 of con.-

vection heater 24 passes from that heater through pipe 43 into the innerrow of tubes of bank 38 of heater 8 and is there rapidly raised intemperature: it is next passed through a soaking section consisting ofthe outer row of tubes and is then discharged through outlet 46. Gas oilintroduced through inlet 44 is similarly heated in the convection heater24 and in bank 31, after which it leaves the heater 8 through outlet 41.The soaking action in the outer row of tubes of banks 31 and 38 permitsof cracking to a greater extent than is possible in bank 36. Bank 39 isadvantageously used to crack naphtha, the naphtha being introduced tothe inner row of tubes through inlet 48 and there brought up to crackingtemperature. Subsequently, this naphtha is passed through the outer rowof tubes where it soaks for an appreciable time at high temperature, andit is finally discharged through outlet 49.

The heaters so far described employ vertical tubes. This I regard as themost useful construction for general purposes. For some purposes,however, it is advantageous to have part of or all the tubes arrangedhorizontally. The same advantages of high efficiency and uniformity ofheating accrue.

Figs. 8, 9 and 10 illustrate diagrammatically alternative tubearrangements within the scope of the invention, some of the tubes beingarranged horizontally. In Figs. 8 and 9 the tube banks comprise a bank60 of horizontal tubes on "each side of the furnace wall (9). The endsof the tubes extend beyond the wall and are pro- .vided with returnbends I4. The end tubes are arranged vertically in banks 6|, extendingbeyond the furnace roof (l2) and floor (l3) as shown and also providedwith return bends 14. This arrangement makes for simple construction andallows easy cleaning of the tubes from the outside of the furnaceproper. The four tube 'hanks form a sort of rectangular cage, as shown.

A row of burners 21 in refrmtory burner cones 26 is provided as in theother embodiments. The burners are equally spaced from each other andfrom the walls of the tube cage, as shown.

Referring to Fig. 9, each bank of tubes on each wall is shown as havingseparate liquid connections 62. This arrangement aFlows four separatestocks to be simultaneously treated in the heater. The banks can beinterconnected in any way desired. It is sometimes convenient to connectthe end banks in series, and run a stream through them in series.

Fig. 10 shows a modification analogous to the structure of Fig. 2,having approximately semicircular ends. The end tubes are arrangedvertically in banks 62, as shown, and the side tubes are arranged in ahorizontal bank. This modification is useful in certain installations.

These modifications work similarly to those in Figs. 1 to '7. If desiredthe tube banks may be subdivided to provide for separate heatingoperations.

While the specific embodiments of my invention herein described areadvantageous for certain purposes, it is to be understood that theinvention is not limited thereto. The tubes may be connected in anydesired manner to give the required number of units and the tubes may beso spaced as to yield the desired heating characteristics. The heatingof other material than petroleum stock is within the purview of myinvention.

In general, the vertical tube arrangement as illustrated in Figs. 1 to 7has the greatest allaround utility.

The essence of my invention is a tubular heater, heated by a pluralityof burners, wherein the tubes of the heater are positioned closely aboutthe 5 plurality of burners to receive radiant heat from the flamesthereof, and-wherein the individual burners are so positioned withrespect to one another that the flames from the individual burners willshield one another from the tubes of the 10 heater only to a minimumdegree. I regard as the best embodiment of my invention a constructionin which the individual burners are positioned in one straight row, andin which a majority of the radiant heater tubes are positioned in twoplanes parallel to one another and to the plane of the burner flames,the heater .tube planes being substantially equally distant from and onopposite sides of the flame plane.

The width of the heater is determined by the 20 effective generation ofheat by the burners, that is, by the nature, shape and characteristicsof the flame produced thereby. The separation between the burners andthe tube bank and accordingly the width of the furnace is approximatelythe same for burners of the same capacity and kind. Greater heatercapacity, when required, is obtained by lengthening the furnacehorizontally and providing additional burners arranged as described. Inthis way the capacity of a furnace may be increased several fold whilenot increasing the spacing between burners and tubes and not increasingthe cross span between the columns which support the superstructure.When a convection heater is used, its shape advantageously conformssubstantially to the shape of the fire chamber or radiant section.though the convection heater is not necessarily of equal dimensions. Theinvention thus permits constructions with fewer dead areas than arepresent in a cylindrical fire heater surrounded by a rectangularconvection section and it also permits a considerable reduction in theamount of refractory material in the furnace roof. The tubes in theconvection section may be made longer 45 than with a circular typefurnace as they may be positioned along the length of the fire chamber.Also, less tube surface is required as the radiant heat produced by theburners is fully utilized in the furnace proper.

In this specification and in the appended claims, I speak of a pluralityof tubes positioned in a symmetrical row about a straight row ofburners. In this connection I use the term symmetrica in its customarysense except that two portions of 65 the tube row shall be substantiallystraight, on opposite sides of the burner row, and substantiallyparallel thereto and substantially equidistant therefrom.

This application is a continuation in part of 60 my prior application,Serial No. 716,439, filed March 19, 1934.

What I claim is:

1. In a tube heater, a plurality of means for producing radiant heat andradiating it laterally, 65 said means being positioned substantiallyequidistant from one another in a straight horizontal row, a pluralityof heat absorbing tubes positioned to form a vertical-walled cage aboutsaid means for producing radiant heat and receiving radiant 70 heattherefrom, the end walls and side walls of said cage being spaced fromthe row of means for producing radiant heat by a distance substantiallyequal to the distance between the means for producing radiant heat.

2. The apparatus of claim 1 wherein the tubes are positioned verticallyin the vertical-walled cage.

3. In a tube still of the type described, a closed row of parallel heatabsorbing tubes and a row comprising a plurality of burners inside saidrow of tubes, everywhere substantially equidistant therefrom and closelyspaced with respect thereto and directly opposed to the tubes, theburners being everywhere substantially equally spaced from each otherand from the tubes.

4. In the apparatus of claim 1, a convection heater positioned above thecage of heat absorbing tubes, the heater being smaller than and of shapegenerally similar to the cage, and passage means leading from theinterior of the tube row to the heater.

5. In a tube heater a plurality of straight heat absorbing tubespositioned vertically at intervals in a row, said row being in the formof a rectangle having two long sides and two short ends, and a pluralityof radiant heat producing burners positioned at intervals in a straighthorizontal row on a vertical plane coinciding with the major axis ofsaid rectangle, the spacing between burners and the spacing of the rowof burners from the sides and ends of the rectangular row of tubes beingsubstantially the same.

6. In a tube still or the like a row of vertical heat absorbing tubes,said row being arranged in the form of an oblong having two straightparallel sides joined at either end by semi-circular ends and a straighthorizontal row of burners adapted to produce radiant heat, said burnerrow being parallel to and equidistant from said parallel sides, and eachend burner in the row being located at the approximate center of onesemicircular end.

7. In the-fire chamber of a vertical tube still, a floor of refractorymaterial, a plurality of burners positioned in .a straight horizontalrow within said floor and adapted to produce radiant heat 'in saidchamber by combustion of suitable fuel,

a plurality of vertical heat absorbing tubes positioned in a row inwhich each tube is spaced from .adjacent tubes, said row of tubes beingsymmetrically arranged around said row of burners and spaced therefromby a short substantially equidistant interval, to insure efficientcombustion and efiective absorption of heat from said burners andrefractory walls forming the side walls of the chamber and enclosingsaid tubes.

8. In a tube heater, a row of vertical, spaced tubes arranged in theshape of .an oblong having two parallel straight sides and substantiallysemicircular ends in combination with a plurality of radiant heatproducing burners arranged at intervals in a straight horizontal rowalong the major vertical axial plane of the space enclosed by saidtubes, said burner row being substantially the same distance from thetubes forming the respective ends of the oblong as it is from the tubesforming the sides of the oblong.

9. In a tube heater, a plurality of heat absorbing tubes positioned inthe form of a verticalwalled cage having two ends and two sides, thetubes being arranged horizontally in the sides and vertically in theends, a plurality of means for producing radiant heat and radiating itlaterally upon the tubes, said means for producing radiant heat beingpositioned substantially equidistant from one another in a straighthorizontal row along the center line of the cage, the end walls and sidewalls of the cage being spaced from the row of means for producingradiant heat by a distance substantially equal to the distance betweenthe means for producing radiant heat.

10. In a tube heater, a plurality of burners for producing radiant heatand radiating it laterally, said burners being positioned substantiallyequidistant from one another in a straight horizontal row, a pluralityof heat absorbing tubes positioned to form a vertical-walled cage aboutsaid burners and receiving radiant heat therefrom, the end walls andside walls of said cage being spaced from the row of burners by adistance substantially equal to the distance between the burners, an airheater positioned above the cage of heat absorbing tubes, and flaringpassage means leading from the interior of the cage to the heater, theair heater being heated by waste products from the burners.

11. In a tube heater, a plurality of means for producing radiant heatand radiating it laterally, said means being positioned substantiallyequidistant from one another in a straight horizontal row, a pluralityof heat absorbing tubes positioned to form a vertical walled cage aboutsaid means for producing radiant heat and receiving radiant heattherefrom, the cage being divided into separate sections each opposed toa different portion of the burner row so that different fluids can bepassed through the sections and be simultaneously heated by the meansfor producing radiant heat, the end walls and side walls of said cagebeing spaced from the row of means for producing radiant heat by adistance substantially equal to the distance between the means forproducing radiant heat.

POVL OSTERGAARD.

